Immunity to Schistosomiasis: Role of Eosinophils in parasite killing and in tissue injury

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Abstract

Eosinophilia is associated with helminth infections and or
allergic conditions. However, the precise role of this cell • has, until recently, been speculative. There is accumulating
evidence to suggest that eosinophils may be involved in the
expression of immunity to parasites; On the other hand
eosinophils have been implicated in various allergic and
inflammatory conditions. If eosinophil dependent immune
mechanisms were, for example, to be incorporated into the
desiqn of a schistosome vaccine, it is imperative that there is
does not result in adverse reactions. This study has thus set
out to examine the relationship between eosinophil levels,
immune mediators, and the ability to kill schistosomula of
Schistosoma metisoni in vitro, in patients treated for S.
menson: in fections. The potential role of eosinophils III
inflammatory responses has been studied by assesing their
ability to adhere and cause damaqe, to cultured human
" umbilical vein endothelial cells (E.C.). Patients for the study
were recruited from outpatient clinics after a positive
diagnosis for S. mansoni infections or for mild allergic
eosin oph il ia. Celis were pu r ifi ed on discontinous
metrizamide gradients to yield highly enriched fractions of
mon onucle ar cells, neutr oph ils, and eosin ophils. Serurn
samples were retained to assay for antibodies to crude
parasite antigens. Antibody dependent schistosomula killing
was estimated by visual microscopy; Anti-parasite
antibodies, and cytokines were measured by elisa; Adherence
and damage to endothelial cells by isotope uptake and
release assays. The results indicated that eosinophil levels
were significantly increased in patients treated for S.
manson; infections. In group 1, patient's peripheral blood
eosinophil counts rose from a mean of 17 5/ul before
treatment. to 745/ul at 3 weeks following treatment, and in
group 2 from 181 lul to 1066/ul. The increase in eosinophil
levels was positively correlated with a rise in circulating
anti-adult worm antibodies (r = 0.587, P <0.05). Despite some
enhanced eosinophil helminthotoxicity following treatment
in some of the individuals In group 1 (7/15), the change
overall was not significant. In group 2, in which a different
standard anti-schistosomular antibody was used, the
eosinophil killing capacity recorded at 3 weeks was lower
than that before commencement of treatment (t = 2.89, P
<0.01). The eosinophil stimulating activity, detected in
cultured mononuclear cells supernatants (MCS) from
individual patients correlated with eosinophil levels (r =
0.582, P <0.02). IL-5 levels in MCS were correlated with
anti-egg antibodies (r = 2.294 P < 0.05). These results .
indicate that peripheral-blood eosinophils are increased
following treatment, but their ability to kill schistosome
larvae is variable and may depend on other cell activating
factors; The results also suggest that egg antigens may be
important In the induction of IL-5, in schistosome
infections.